Image decoding device and image coding device

ABSTRACT

A reference picture information decoding unit (13) omits decoding of a reference list sorting presence or absence flag and/or a reference list sorting order based on the number of current picture referable pictures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/222,895, filed Dec. 17, 2018, which is a continuation of U.S.application Ser. No. 15/789,285, filed Oct. 20, 2017, now issued as U.S.Pat. No. 10,194,161, which is a continuation of U.S. application Ser.No. 15/012,597, filed Feb. 1, 2016, now issued as U.S. Pat. No.9,866,856, which is a continuation of U.S. application Ser. No.14/430,249, filed Mar. 23, 2015, now issued as U.S. Pat. No. 9,667,984,which is a 371 of International Application No. PCT/JP2013/076109, filedSep. 26, 2013, which claims the benefit of Japanese Application No.2012-218582, filed Sep. 28, 2012. The entire contents of each of theforegoing applications is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to an image decoding device decoding codeddata indicating an image and an image coding device generating the codeddata by coding the image.

BACKGROUND ART

In order to transmit or record a moving image efficiently, a movingimage coding device generating coded data by coding the moving image anda moving image decoding device generating a decoded image by decodingthe coded data are used.

As a specific moving image coding scheme, for example, schemes (seeNPL 1) proposed in H.264/MPEG-4.AVC and High-Efficiency Video Coding(HEVC) which is its successor codec can be exemplified.

In such a moving image coding scheme, an image (picture) forming amoving image is managed with a hierarchical structure configured toinclude a slice obtained by splitting an image, a coding unit (alsoreferred to as a coding unit) obtained by splitting the slice, and ablock and a partition obtained by splitting the coding unit, and isnormally coded/decoded for each block.

In such a moving image coding scheme, generally, a predicted image isgenerated based on a local decoded image obtained by coding/decoding aninput image and a prediction residual (also referred to as a “differenceimage” or a “residual image”) obtained by subtracting the predictedimage from the input image (original image) is coded. As a method ofgenerating a predicted image, inter-screen prediction (inter-prediction)and in-screen prediction (intra prediction) can be exemplified.

In the intra-prediction, predicted images in the same frame aresequentially generated based on local decoded images in the same frame.

In the inter-prediction, predicted images are generated by applyingmotion compensation prediction on reference pictures included in areference picture list. The reference pictures are a subset of localdecoded images in regard to a coded/decoded frame recorded in a picturebuffer. Reference picture specifying information indicating which localdecoded image in the picture buffer is a reference picture is includedin header information. Reference picture order information indicating anorder in which reference pictures are arranged in a reference picturelist is also included in the header information.

CITATION LIST Non Patent Literature

NPL 1: “High efficiency video coding (HEVC) text specification draft 8(JCTVC-J1003_d7),” Joint Collaborative Team on Video Coding (JCT-VC) ofITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11 11th Meeting: Stockholm, SE onJul. 11 to 20, 2012 (disclosed on Jul. 28, 2012)

SUMMARY OF INVENTION Technical Problem

However, there is a problem that the reference picture specifyinginformation and the reference picture order information according to therelated art are not optimum. Specifically, there is a problem that thenumber of reference pictures available in a specific picture is notconsidered and information is redundantly transmitted in transmission ofthe reference picture specifying information and the reference pictureorder information included in the header information.

The present invention is devised in view of the above-mentioned problemand an object of the present invention is to provide an image decodingdevice capable of decoding a moving image or an image coding devicecapable of coding a moving image by transmitting reference picturespecifying information and reference picture order information inconsideration of the number of reference pictures available in aspecific picture and using header information of a smaller codingamount.

Solution to Problem

In order to resolve the above-mentioned problem, according to an aspectof the present invention, there is provided an image decoding devicegenerating a predicted image through motion compensation prediction withreference to one or more reference images recorded on a decoded picturebuffer and using the predicted image in image decoding. The imagedecoding device includes: reference picture set derivation means forderiving a reference picture set to be applied to a target picture;reference picture list generation means for generating a referencepicture list available in the target picture based on reference picturelist (RPL) modification information decoded from a slice header and thereference picture set derived by the reference picture set derivationmeans; and reference picture information decoding means for omittingdecoding of a part of information included in the RPL modificationinformation based on the number of current picture referable pictures.

Advantageous Effects of Invention

According to the aspect of the present invention, the decoding of atleast one of a reference picture list sorting presence or absence flagand a reference list sorting order is omitted based on the number ofcurrent picture referable pictures. Accordingly, it is possible toprevent information regarding the reference picture unnecessary in thedecoding from being transmitted, and thus there is an advantageouseffect capable of decoding a moving image with header information of asmaller coding amount.

According to the aspect of the present invention, the coding of at leastone of the reference picture list sorting presence or absence flag andthe reference list sorting order is omitted based on the number ofcurrent picture referable pictures. Accordingly, it is possible toprevent information regarding the reference picture unnecessary in thedecoding from being transmitted, and thus there is an advantageouseffect capable of generating coded data so that a moving image isdecoded with a header information of a smaller coding amount.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating details of a reference picture listconstruction process according to an embodiment of the presentinvention.

FIG. 2 is a functional block diagram illustrating a schematicconfiguration of a moving image decoding device according to theembodiment of the present invention.

(a) to to (e) of FIG. 3 are diagrams illustrating a sequence layerdefining a sequence SEQ, a picture layer defining a picture PICT, aslice layer defining a slice S, a CTB layer defining a coding tree blockCTB, and a CU layer defining a coding unit (CU) included in the codingtree block CTB, respectively.

FIG. 4 is a diagram illustrating examples of a reference picture set anda reference picture list, (a) of FIG. 4 is a diagram illustratingpictures configuring a moving image and arranged in a display order, (b)of FIG. 4 is a diagram illustrating an example of RPS informationapplied to a target picture, (c) of FIG. 4 is a diagram illustrating anexample of a current RPS derived at the time of application of the RPSinformation exemplified in (b) of FIG. 4 when the POC of the targetpicture is 0, and (d) and (e) of FIG. 4 are diagrams illustratingexamples of reference picture lists generated from reference picturesincluded in the current RPS.

FIG. 5 is a diagram illustrating reference picture list modificationexamples, (a) of FIG. 5 is a diagram illustrating an L0 reference listbefore modification, (b) of FIG. 5 is a diagram illustrating RPLmodification information, and (c) of FIG. 5 is a diagram illustratingthe L0 reference list after the modification.

FIG. 6 is a diagram exemplifying a part of an SPS syntax table used atthe time of decoding of an SPS in a header information decoding sectionand a reference picture information decoding section of the moving imagedecoding device.

FIG. 7 is a diagram exemplifying a syntax table of a short-termreference picture set used at the time of decoding of the SPS and at thetime of decoding of a slice header in the header information decodingsection and the reference picture information decoding section of themoving image decoding device.

FIG. 8 is a diagram exemplifying a part of a slice header syntax tableused at the time of decoding of a slice header in the header informationdecoding section and the reference picture information decoding sectionof the moving image decoding device.

FIG. 9 is a diagram exemplifying a part of the slice header syntax tableused at the time of decoding of a slice header in the header informationdecoding section and the reference picture information decoding sectionof the moving image decoding device.

FIG. 10 is a diagram exemplifying a syntax table of reference listsorting information used at the time of the decoding of the slice headerin the header information decoding section and the reference pictureinformation decoding section of the moving image decoding device.

FIG. 11 is a diagram exemplifying a syntax table of reference listsorting information used at the time of the decoding of the slice headerin the moving image decoding device.

FIG. 12 is a diagram exemplifying another syntax table of the referencelist sorting information used at the time of the decoding of the sliceheader in the moving image decoding device.

FIG. 13 is a diagram exemplifying a syntax table of reference listsorting information used at the time of the decoding of the slice headerin the moving image decoding device.

FIG. 14 is a diagram exemplifying another syntax table of the referencelist sorting information used at the time of the decoding of the sliceheader in the moving image decoding device.

FIG. 15 is a diagram exemplifying still another syntax table of thereference list sorting information used at the time of the decoding ofthe slice header in the moving image decoding device.

FIG. 16 is a diagram exemplifying still another syntax table of thereference list sorting information used at the time of the decoding ofthe slice header in the moving image decoding device.

FIG. 17 is a functional block diagram illustrating a schematicconfiguration of a moving image coding device according to theembodiment of the present invention.

FIG. 18 is a diagram illustrating configuration examples of atransmission apparatus on which the moving image coding device ismounted and a reception apparatus on which the moving image decodingdevice is mounted. (a) of FIG. 18 illustrates the transmission apparatuson which the moving image coding device is mounted and (b) of FIG. 18illustrates the reception apparatus on which the moving image decodingdevice is mounted.

FIG. 19 is a diagram illustrating configuration examples of a recordingapparatus on which the moving image coding device is mounted and areproduction apparatus on which the moving image decoding device ismounted. (a) of FIG. 19 illustrates the recording apparatus on which themoving image coding device is mounted and (b) of FIG. 19 illustrates thereproduction apparatus on which the moving image decoding device ismounted.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described with referenceto FIGS. 1 to 17. First, the overviews of a moving image decoding device(image decoding device) 1 and a moving image coding device (image codingdevice) 2 will be described with reference to FIG. 2. FIG. 2 is afunctional block diagram illustrating a schematic configuration of themoving image decoding device 1.

A technology adopted in the H.264/MPEG-4.AVC standard and a technologyproposed in High-Efficiency Video Coding (HEVC) which is its successorcodec are mounted on the moving image decoding device 1 and the movingimage coding device 2 illustrated in FIG. 2.

The moving image coding device 2 performs entropy coding on the value ofa syntax in which transmission from an encoder to a decoder is definedto generate coded data #1 according to such moving image coding schemes.

The coded data #1 coded from a moving image by the moving image codingdevice 2 is input to the moving image decoding device 1. The movingimage decoding device 1 decodes the input coded data #1 and outputsdecoded moving image #2 to the outside. Before the detailed descriptionof the moving image decoding device 1, the configuration of the codeddata #1 will be described below.

[Configuration of Coded Data]

A configuration example of the coded data #1 generated by the movingimage coding device 2 and decoded by the moving image decoding device 1will be described with reference to FIG. 3. The coded data #1 includes,for example, a sequence and a plurality of pictures configuring thesequence.

A data hierarchical structure of the coded data #1 is illustrated inFIG. 3. (a) to (e) of FIG. 3 are diagrams illustrating a sequence layerdefining a sequence SEQ, a picture layer defining a picture PICT, aslice layer defining a slice S, a CTB layer defining a coding tree blockCTB, and a CU layer defining a coding unit (CU) included in the codingtree block CTB, respectively.

(Sequence Layer)

In the sequence layer, a set of data referred to by the moving imagedecoding device 1 is defined to decode a processing target sequence SEQ(hereinafter also referred to as a target sequence). As illustrated in(a) of FIG. 3, the sequence SEQ includes a sequence parameter set SPS, apicture parameter set PPS, pictures PICT1 to PICTNP (where NP is a totalnumber of pictures included in the sequence SEQ), and supplementalenhancement information SEI.

In the sequence parameter set SPS, a set of coding parameters referredto by the moving image decoding device 1 is defined to decode the targetsequence. The details of the SPS will be described below.

In the picture parameter set PPS, a set of coding parameters referred toby the moving image decoding device 1 is defined to decode each picturein the target sequence. A plurality of PPSs may be present. In thiscase, one of the plurality of PPSs is selected from the pictures in thetarget sequence.

(Picture Layer)

In the picture layer, a set of data referred to by the moving imagedecoding device 1 is defined to decode the processing target picturePICT (hereafter also referred to as a target picture). As illustrated in(b) of FIG. 3, the picture PICT includes a plurality of slices, that is,slices S1 to SNS (where NS is a total number of slices included in thepicture PICT).

When it is not necessary to distinguish the slices S1 to SNS from eachother, the slices are described below in some cases by omitting thesubscripts of the codes. The same also applies to data which is dataincluded in the coded data #1 to be described below and is other data towhich subscripts are appended.

(Slice Layer)

In the slice layer, a set of data referred to by the moving imagedecoding device 1 is defined to decode the processing target slice S(also referred to as a target slice). As illustrated in (c) of FIG. 3,the slice S includes a slice header SH and a sequence of coding treeblocks CTB1 to CTBNC (where NC is a total number of coding tree blocksincluded in the slice S).

The slice header SH includes a coding parameter group referred to by themoving image decoding device 1 to decide a method of decoding the targetslice. Slice type designation information (slice_type) designating thetypes of slices is an example of a coding parameter included in theslice header SH.

As the types of slices which can be designated by the slice typedesignation information, for example, (1) an I slice using onlyintra-prediction at the time of coding, (2) a P slice usinguni-directional prediction or intra-prediction at the time of coding,and (3) a B slice using uni-directional prediction, bi-directionalprediction, or intra-prediction at the time of coding can beexemplified.

The slice header SH may include a reference (pic_parameter_set_id) inthe picture parameter set PPS included in the sequence layer.

(CTB Layer)

In the CTB layer, a set of data referred to by the moving image decodingdevice 1 is defined to decode a processing target coding tree block CTB(hereinafter also referred to as a target CTB). The CTB is also referredto as a largest coding unit (LCU) or a tree block in some cases.

The coding tree block CTB includes a CTB header CTBH and pieces ofcoding unit information CU1 to CUNL (where NL is a total number ofpieces of coding unit information included in the CTB). The coding unitinformation CU is associated with a coding unit which is a partialregion obtained by splitting the CTB. Hereinafter, the coding unit isreferred to as a CU (coding unit). The CU is also referred to a codingblock (CB) in some cases.

(CTB Header)

The CTB header CTBH includes a coding parameter referred to by themoving image decoding device 1 to decide a method of decoding the targetCTB. Specifically, as illustrated in (d) of FIG. 3, the CTB header CTBHincludes CTB splitting information SP_CTB designating a splittingpattern in which the target CTB is split into each CU and a quantizationparameter difference Δqp (qp_delta) designating the magnitude of aquantization step.

The CTB splitting information SP_CTB is information that indicates acoding tree for splitting the CTB. Specifically, the CTB splittinginformation SP_CTB is information that designates the shape and size ofeach CU included in the target CTB and the position of each CU in thetarget CTB.

The quantization parameter difference Δqp is a difference qp−qp′ betweena quantization parameter qp in the target CTB and a quantizationparameter qp′ in the CTB coded immediately before the target CTB.

(CU Layer)

In the CU layer, a set of data referred to by the moving image decodingdevice 1 is defined to decode the processing target CU (hereinafter alsoreferred to as a target CU).

Here, a tree structure of data included in the CU will be describedbefore the description of the specific contents of the data included inthe coding unit information CU. A coding node is a node of the roots ofa prediction tree (PT) and a transform tree (TT). The prediction treeand the transform tree will be described as follows.

In the prediction tree, the coding node is split into one predictionblock or a plurality of prediction blocks, and the position and size ofeach prediction block are defined. In other words, the prediction blockis one region or a plurality of non-overlapping regions configuring thecoding node. The prediction tree includes one prediction block or aplurality of prediction block obtained through the above-describedsplitting.

A prediction process is performed for each prediction block.Hereinafter, the prediction block which is a unit of prediction is alsoreferred to as a prediction unit (PU).

In the transform tree, the coding node is split into one transform blockor a plurality of transform blocks, and the position and size of eachtransform block are defined. In other words, the transform block is oneregion or a plurality of non-overlapping regions configuring the codingnode. The transform tree includes one transform block or the pluralityof transform blocks obtained through the above-described splitting.

A transform process is performed for each transform block. Hereinafter,the transform block which is a unit of transform is also referred to asa transform unit (TU).

(Data Structure of Coding Unit Information)

Next, the specific contents of data included in the coding unitinformation CU will be described with reference to (e) of FIG. 3. Asillustrated in (e) of FIG. 3, the coding unit information CUspecifically includes a skip mode flag SKIP, a CU prediction typeinformation Pred_type, PT information PTI, and TT information TTI.

[Skip Flag]

The skip mode flag SKIP is a flag that indicates whether a skip mode isapplied to the target CU. When the value of the skip mode flag SKIP is1, that is, the skip mode is applied to the target CU, the PTinformation PTI is omitted in the coding unit information CU. The skipmode flag SKIP is omitted in the I slice.

[CU Prediction Type Information]

The CU prediction type information Pred_type includes CU predictionscheme information PredMode and PU splitting type information PartMode.

The CU prediction scheme information PredMode is used to designate oneof intra-prediction (intra CU) and inter-prediction (inter CU) as apredicted image generation method for each PU included in the target CU.Hereinafter, classification of skip, intra-prediction, andinter-prediction in the target CU is referred to as a CU predictionmode.

The PU splitting type information PartMode is used to designate a typeof PU splitting which is a pattern in which the target coding unit (CU)is split into each PU. Thus, hereinafter splitting of the target codingunit (CU) into each PU according to the type of PU splitting is referredto as PU splitting.

The selectable type of PU splitting differs depending on a CU predictionscheme and a CU size. More specifically, the selectable type of PUsplitting differs between the cases of the inter-prediction and theintra-prediction. The details of the type of PU splitting will bedescribed below.

[PT Information]

The PT information PTI is information regarding a PT included in thetarget CU. In other words, the PT information PTI is a set ofinformation regarding one PU or each of the plurality of PUs included inthe PT. As described above, since a predicted image is generated usingthe PU as a unit, the PT information PTI is referred to when thepredicted image is generated by the moving image decoding device 1. Asillustrated in (e) of FIG. 3, the PT information PTI includes pieces ofPU information PUI1 to PUINP (where NP is a total number of PUs includedin the target PT) including prediction information in each PU.

The prediction information PUI includes intra-prediction information orinter-prediction information depending on which prediction method theprediction type information Pred_mode designates. Hereinafter, the PUapplied to the intra-prediction is referred to as an intra PU and the PUapplied to the inter-prediction is referred to as an inter PU.

The inter-prediction information includes motion compensation parametersreferred to when the moving image decoding device 1 generates aninter-predicted image through inter-prediction.

As the motion compensation parameters, for example, a merge flag(merge_flag) a merge index (merge_idx), an estimation motion vectorindex (mvp_idx), a reference image index (ref_idx), an inter-predictionflag (inter_pred_flag), and a motion vector residual (mvd) can beexemplified.

The intra-prediction information includes coding parameters referred towhen the moving image decoding device 1 generates an intra-predictionimage through intra-prediction.

As the intra-prediction parameters, for example, an estimationprediction mode flag, an estimation prediction mode index, and aresidual prediction mode index can be exemplified.

[TT Information]

The TT information TTI is information regarding the TT included in theCU. In other words, the TT information TTI is a set of informationregarding one TU or each of the plurality of TUs included in the TT andis referred to when the moving image decoding device 1 decodes residualdata. Hereinafter, the TU is also referred to as a transform block.

As illustrated in (e) of FIG. 3, the TT information TTI includes TTsplitting information SP_TU used to designate a splitting pattern inwhich the target CU is split into each transform block and pieces of TUinformation TUI1 to TUINT (where NT is a total number of blocks includedin the target CU).

The TT splitting information SP_TU is specifically information used todecide the shape and the size of each TU included in the target CU andthe position of the TU in the target CU. For example, the TT splittinginformation SP_TU can be realized from information(split_transform_flag) indicating whether the splitting of the targetnode is performed and information (trafoDepth) indicating a depth of thesplitting.

For example, when the size of the CU is 64×64, each TU obtained throughthe splitting can have a size from 32×32 pixels to 4×4 pixels.

The pieces of TU information TUI1 to TUINT are individual pieces ofinformation regarding one TU or each of the plurality of TUs included inthe TT. For example, the TU information TUI includes quantizationprediction residuals.

Each quantization prediction residual is coded data generated when themoving image coding device 2 performs the following processes 1 to 3 ona target block which is a processing target block.

Process 1: a prediction residual obtained by subtracting a predictedimage from a coding target image is subjected to Discrete CosineTransform (DCT).

Process 2: a transform coefficient obtained in process 1 is quantized.

Process 3: the transform coefficient quantized in process 2 is subjectedto variable-length coding.

The above-described quantization parameter qp indicates the magnitude ofa quantization step QP used when the moving image coding device 2quantizes the transform coefficient (QP=2qp/6).

[Moving Image Decoding Device]

Hereinafter, the configuration of the moving image decoding device 1according to the embodiment will be described with reference to FIGS. 1to 16.

(Overview of Moving Image Decoding Device)

The moving image decoding device 1 generates a predicted image in eachPU, adds the generated predicted image and the prediction residualdecoded from the coded data #1 to generate the coded image #2, andoutputs the generated decoded image #2 to the outside.

Here, the predicted image is generated referring to the codingparameters obtained by decoding the coded data #1. The coding parametersrefer to parameters which are referred to in order to generate apredicted image. The coding parameters include not only motioninformation (for example, a motion vector, a reference image, referenceimage list selection information, and motion compensation methodselection information) referred to in inter-screen prediction or aprediction parameter such as a prediction mode referred to in theinter-screen prediction but also the size or shape of the PU, the sizeor shape of the block, and residual data between an original image and apredicted image.

Hereinafter, the picture (frame), the slice, the CTB, the block, and thePU to be decoded are referred to as a target picture, a target slice, atarget CTB, a target block, and a target PU, respectively.

(Configuration of Moving Image Decoding Device)

A schematic configuration of the moving image decoding device 1 will bedescribed below with reference to FIG. 2. FIG. 2 is a functional blockdiagram illustrating a schematic configuration of the moving imagedecoding device 1.

As illustrated in FIG. 2, the moving image decoding device 1 includes aheader decoding section 10, a picture decoding section 11, a decodedpicture buffer 12, a reference picture set derivation section 14, and areference picture list derivation section 15. The header decodingsection 10 includes a reference picture information decoding section 13therein.

[Header Decoding Section]

The header decoding section 10 decodes information used to decode thecoded data #1 supplied from the moving image coding device 2 in thesequence unit, the picture unit, or the slice unit. The decodedinformation is output to constituent elements of the moving imagedecoding device 1 including the picture decoding section 11.

The header decoding section 10 parses the SPS included in the coded data#1 based on the given syntax information and decodes the informationused for the decoding in the sequence unit. For example, informationrelated to the image size of a decoded image is decoded from the SPS.

The header decoding section 10 parses the slice header included in thecoded data #1 based on the given syntax definition and decodesinformation used for the decoding in the slice unit. For example, thetype of slice is decoded from the slice header.

[Reference Picture Information Decoding Section]

The reference picture information decoding section is a constituentelement of the header decoding section 10 and decodes informationregarding the reference picture from the coded data #1. The informationregarding the reference picture includes reference picture setinformation (hereinafter referred to as RPS information) and referencepicture list modification information (hereinafter referred to as RPLmodification information).

The reference picture set (RPS) indicates a set of pictures which islikely to be used as a reference picture in the target picture or in apicture subsequent to the target picture in the decoding order. The RPSinformation is information that is decoded from the SPS or the sliceheader and is information that is used to derive the reference pictureset that is set at the time of the decoding of each picture.

The reference picture list (RPL) is a list of candidates of thereference picture to be referred to when motion compensation predictionis performed. Two or more reference picture lists may be present. In theembodiment, an L0 reference picture list (L0 reference list) and an L1reference picture list (L1 reference list) are assumed to be used. TheRPL modification information is information that is decoded from the SPSor the slice header and indicates an order of the reference pictures inthe reference picture list.

In the motion compensation prediction, the reference picture recorded atthe position of the reference image index (refIdx) on the referenceimage list is used. For example, when the value of refIdx is 0, theposition of 0 of the reference image list, that is, the referencepicture in the beginning of the reference image list, is used for themotion compensation prediction.

Since a decoding process for the RPS information and the RPLmodification information by the reference picture information decodingsection 13 is an important process in the embodiment, the decodingprocess will be described in detail later.

Here, examples of the reference picture set and the reference picturelist will be described with reference to FIG. 4. In (a) of FIG. 4,pictures configuring a moving image are arranged in a display order areillustrated and a numeral in the drawing indicates a POC correspondingto each picture in the drawing. As will be described below indescription of the decoded picture buffer, the POC is assigned to eachpicture in an ascending order of output. The POC of 9 indicated by“curr” is a current decoding target picture.

(b) of FIG. 4 illustrates an example of the RPS information applied tothe target picture. The reference picture set (current RPS) in thetarget picture is derived based on the RPS information. The RPSinformation includes long-term RPS information and short-term RPSinformation. As the long-term RPS information, the POC of the pictureincluded in the current RPS is directly shown. In the exampleillustrated in (b) of FIG. 4, the long-term RPS information indicatesthat the picture of POC=1 is included in the current RPS. In theshort-term RPS information, the picture included in the current RPS isrecorded with a difference in regard to the POC of the target picture.The short-term RPS information indicated by “Before, dPOC=1” indicatesthat the picture of the POC smaller by 1 than the POC of the targetpicture is included in the current RPS. Likewise, “Before, dPOC=4” inthe drawing indicates that the picture of the POC is smaller than 4 and“After, dPOC=1” indicates that the picture of the POC larger by 1 isincluded in the current RPS. “Before” indicates the front of the targetpicture, that is, the picture earlier than the target picture in thedisplay order. “After” indicates the rear of the target picture, thatis, the picture later than the target picture in the display order.

(c) of FIG. 4 illustrates an example of the current RPS derived at thetime of application of the RPS information exemplified in (b) of FIG. 4when the POC of the target picture is 0. The picture of POC=1 indictedby the long-term RPS information is included. The picture that is shownin the short-term RPS information and has the POC smaller by 1 than thetarget picture (POC=9), that is, the picture of POC=8, is included.Likewise, the pictures of POC=5 and POC=10 shown in the short-term RPSinformation are included.

(d) and (e) of FIG. 4 illustrate examples of the reference picture listsgenerated from the reference pictures included in the current RPS. Anindex (reference picture index) is assigned to each element of thereference picture list (the index is written as idx in the drawing). (d)of FIG. 4 illustrates an example of the L0 reference list. In the L0reference list, the reference pictures with the POCs of 5, 8, 10, and 1included in the current RPS are included in this order. (e) of FIG. 4illustrates an example of the L1 reference list. In the L1 referencelist, the reference pictures with the POCs of 10, 5, and 8 included inthe current RPS are included in this order. As illustrated in theexample of the L1 reference list, it is not necessary to include all ofthe reference pictures (referable pictures) included in the current RPSin the reference picture list. However, the number of elements of thereference picture list is the number of reference pictures included inthe current RPS at most. In other words, the length of the referencepicture list is equal to or less than the number of referable pictureswhich are current pictures.

Next, an example of reference picture list modification will bedescribed with reference to FIG. 5. FIG. 5 exemplifies a referencepicture list ((c) of FIG. 5) after modification which can be obtainedwhen RPL modification information ((b) of FIG. 5) is applied to aspecific reference picture list ((a) of FIG. 5). The L0 reference listbefore modification illustrated in (a) of FIG. 5 is the same as the L0reference list described in (d) of FIG. 4. The RPL modificationinformation illustrated in (b) of FIG. 5 is configured as a list inwhich the values of the reference picture indexes are elements, andvalues 0, 2, 1, and 3 are stored in order from the beginning. The RPLmodification information indicates that the reference pictures indicatedby the reference picture indexes of 0, 2, 1, and 3 included in thereference list before modification are configured as reference picturesof an L0 reference list after modification in this order. (c) of FIG. 5illustrates the L0 reference list after modification and the pictureswith the POCs of 5, 10, 8, and 1 are included in this order.

[Picture Decoding Section]

The picture decoding section 11 generates a local decoded image of eachpicture based on the coded data #1, the header information input fromthe header decoding section 10, the reference picture recorded on thedecoded picture buffer 12, and the reference picture list input from thereference picture list derivation section 15 and records the localdecoded image on the decoded picture buffer 12.

A summary of the decoding order of a specific picture (target picture)in the picture decoding section 11 is as follows.

(S101) The CTBs configuring the target picture are set sequentially asthe target CTBs. Processes of S102 to S106 are performed on each CTB.Thereafter, a process of S107 is performed.

(S102) The CTB splitting information regarding the target CTB is decodedfrom the coded data #1.

(S103) The CUs configuring the target CTB are set sequentially as thetarget CUs and the following processes of S104 to S1106 are performed.

(S104) The CU prediction type information and PU splitting informationof the target CU are decoded. When the target CU is the inter CU or theskip CU, S104 a 1 to S104 a 5 are performed. On the other hand, when thetarget CU is the intra CU, S104 b 1 is performed.

(S104 a 1) The PUs configuring the target CU are set sequentially as thetarget PUs and the following processes are performed.

(S104 a 2) The motion information regarding the target PU is decoded.

(S104 a 3) When L0 prediction is used for the target PU, the referencepicture located at a position indicated by the L0 reference index in theL0 reference list is set as the reference picture of the target PU. AnL0 predicted image is generated based on a decoding pixel value of thereference picture indicated by an L0 motion vector.

(S104 a 4) When L1 prediction is used for the target PU, the referencepicture located at a position indicated by the L1 reference index in theL1 reference list is set as the reference picture of the target PU. AnL1 predicted image is generated base on a pixel value located at aposition indicated by an L1 motion vector in the reference picture.

(S104 a 5) When only the L0 prediction is used for the target PU, the L0predicted image is configured as a predicted image of the target PU. Onthe other hand, when only the L1 prediction is used for the target PU,the L1 predicted image is configured as a predicted image of the targetPU. On the other hand, when both of the L0 prediction and the L1prediction are used for the target PU (when bi-prediction is used), aweighted average of the L0 predicted image and the L1 predicted image isconfigured as a predicted image of the target PU.

(S104 b 1) An intra-prediction mode corresponding to each PU configuringthe target CU is decoded and a predicted image is generated based on anintra-prediction method corresponding to each intra-prediction mode.

(S105) The TT information regarding the target CU is decoded. For eachTU configuring the target CU, a transform coefficient is decoded. Aprediction residual is generated by applying inverse quantization andinverse transform to the transform coefficient.

(S106) The prediction residual is added to the predicted image togenerate a local decoded image before filter application to the targetCU.

(S107) An adaptive offset filter and a deblocking filter are applied tothe local decoded image before filter application to the target pictureto configure a local decoded image of the target picture.

[Decoded Picture Buffer]

The local decoded image of each picture decoded by the picture decodingsection is recorded in association with a picture order count (POC:picture order information) of the picture on the decoded picture buffer12. The decoded picture buffer 12 decides the POC of an output target ata predetermined output timing. Thereafter, the local decoded imagecorresponding to the POC is output as one of the pictures configuringthe decoded image #2 to the outside.

[Reference Picture Set Setting Section]

The reference picture set setting section 14 constructs the referencepicture set RPS based on the RPS information decoded by the referencepicture information decoding section 13 and information regarding thePOC and the local decoded image recorded on the decoded picture buffer12, and then outputs the reference picture set RPS to the referencepicture list derivation section 15. The details of the reference pictureset setting section 14 will be described below.

[Reference Picture List Derivation Section]

The reference picture list derivation section 15 generates the referencepicture list RPL based on the RPL modification information decoded bythe reference picture information decoding section 13 and the referencepicture set RPS input from the reference picture set setting section 14,and then outputs the reference picture list RPL to the picture decodingsection 11. The details of the reference picture list derivation section15 will be described below.

(Order of Moving Image Decoding Process)

An order in which the decoded image #2 is generated from the input codeddata #1 by the moving image decoding device 1 is as follows.

(S11) The header decoding section 10 decodes the SPS from the coded data#1.

(S12) The header decoding section 10 decodes the PPS from the coded data#1.

(S13) The pictures indicated by the coded data #1 are set sequentiallyas the target pictures. Processes of S14 to S17 are performed on eachtarget picture.

(S14) The header decoding section 10 decodes the slice header of eachslice included in the target picture from the coded data #1. Thereference picture information decoding section 13 included in the headerdecoding section 10 decodes the RPS information from the slice headerand outputs the RPS information to the reference picture set settingsection 14. The reference picture information decoding section 13decodes the RPL modification information from the slice header andoutputs the RPL modification information to the reference picture listderivation section 15.

(S15) The reference picture set setting section 14 generates thereference picture set RPS to be applied to the target picture based onthe RPS information and a combination of the POC of the local decodedimage recorded on the decoded picture buffer 12 and positionalinformation in a memory, and then outputs the reference picture set RPSto the reference picture list derivation section 15.

(S16) The reference picture list derivation section 15 generates thereference picture list RPL based on the reference picture set RPS andthe RPL modification information and outputs the reference picture listRPL to the picture decoding section 11.

(S17) The picture decoding section 11 generates the local decoded imageof the target picture based on the slice data of each slice included inthe target picture and the reference picture list RPL from the codeddata #1 and records the local decoded image on the decoded picturebuffer in association with the POC of the target picture. The localdecoded image recorded on the decoded picture buffer is output as thedecoded image #2 to the outside at a proper timing decided based on thePOC.

(Details of Reference Picture Information Decoding Process)

The details of a decoding process for the RPS information and the RPLmodification information in the process of S14 in the decoding orderwill be described.

(RPS Information Decoding Process)

The RPS information is information that is decoded from the SPS or theslice header to construct the reference picture set. The RPS informationincludes the following:

1. SPS short-term RPS information: short-term reference picture setinformation included in the SPS;

2. SPS long-term RP information: long-term reference picture informationincluded in the SPS;

3. SH short-term RPS information: short-term reference picture setinformation included in the slice header; and

4. SH long-term RP information: long-term reference picture informationincluded in the slice header.

(1. SPS Short-Term RPS Information)

The SPS short-term RPS information includes information regarding aplurality of short-term reference picture sets which can be used fromeach picture in which the SPS is referred to. The short-term referencepicture set is a set of pictures that can be reference pictures(short-term reference pictures) designated by relative positions (forexample, POC differences from the target picture) with respect to thetarget picture.

The decoding of the SPS short-term RPS information will be describedwith reference to FIG. 6. FIG. 6 exemplifies a part of an SPS syntaxtable used at the time of SPS decoding in the header informationdecoding section 10 and the reference picture information decodingsection 13. A part (A) of FIG. 6 corresponds to the SPS short-term RPSinformation. The SPS short-term RPS information includes the number ofshort-term reference picture sets (num_short_term_ref_pic_sets) includedin the SPS and each piece of short-term reference picture setinformation (short_term_ref_pic_set(i)).

The short-term reference picture set information will be described withreference to FIG. 7. FIG. 7 exemplifies a syntax table of the short-termreference picture set used at the time of the decoding of the SPS andthe decoding of the slice header in the header information decodingsection 10 and the reference picture information decoding section 13.

The short-term reference picture set information includes the number ofshort-term reference pictures (num_negative_picts) of which a displayorder is earlier than that of the target picture and the number ofshort-term reference pictures (num_positive_pics) of which a displayorder is later than that of the target picture. Hereinafter, theshort-term reference picture of which the display order is earlier thanthat of the target picture is referred to as a front short-termreference picture and the short-term reference picture of which thedisplay order is later than that of the target picture is referred to asa rear short-term reference picture.

The short-term reference picture set information includes an absolutevalue of the POC difference from the target picture(delta_poc_s0_minus1[i]) and presence or absence of possibility to beused as the reference picture of the target picture(used_by_curr_pic_s0_flag[i]) for each front short-term referencepicture. The short-term reference picture set information furtherincludes an absolute value of the POC difference from the target picture(delta_poc_s1_minus1[i]) and presence or absence of possibility to beused as the reference picture of the target picture(used_by_curr_pic_s1_flag[i]) for each rear short-term referencepicture.

(2. SPS Long-Term RP Information)

The SPS long-term RP information includes information regarding theplurality of long-term reference pictures which can be used from eachpicture in which the SPS is referred to. The long-term reference picturerefers to a picture designated by an absolute position (for example, thePOC) within the sequence.

Referring back to FIG. 6, the decoding of the SPS long-term RPinformation will be described. A part (B) of FIG. 6 corresponds to theSPS long-term RP information. The SPS long-term RP information includesinformation (long_term_ref_pics_present_flag) indicating whether thereis the long-term reference picture to be transmitted with the SPS, thenumber of long-term reference pictures included in the SPS(num_long_term_ref_pics_sps), and information regarding each long-termreference picture. The information regarding the long-term referencepicture includes the POC of the reference picture(lt_ref_pic_poc_lsb_sps[i]) and presence or absence of possibility to beused as the reference picture of the target picture(used_by_curr_pic_lt_sps_flag[i]).

The POC of the reference picture may be the value itself of the POCassociated with the reference picture, or at least significant bit (LSB)of the POC, that is, a remaining value obtained by dividing the POC by agiven square of 2, may be used.

(3. SH Short-Term RPS Information)

The SH short-term RPS information includes information regarding thesingle short-term reference picture set which can be used from thepicture in which the slice header is referred to.

The decoding of the SPS short-term RPS information will be describedwith reference to FIG. 8. FIG. 8 exemplifies a part of a slice headersyntax table used at the time of the decoding of the slice header in theheader information decoding section 10 and the reference pictureinformation decoding section 13. A part (A) of FIG. 8 corresponds to theSH short-term RPS information. The SH short-term RPS informationincludes a flag (short_term_ref_pic_set_sps_flag) indicating whether theshort-term reference picture set is selected from the short-termreference picture sets decoded with SPS or is explicitly included in theslice header. When the short-term reference picture set is selected fromthe short-term reference picture sets decoded with the SPS, anidentifier (short_term_ref_pic_set_idx) indicating that one the decodedshort-term reference picture sets is selected is included. When theshort-term reference picture set is explicitly included in the sliceheader, information corresponding to the syntax table(short_term_ref_pic_set(idx)) described above with reference to FIG. 7is included in the SPS short-term RPS information.

(4. SH Long-Term RP Information)

The SH long-term RP information includes information regarding thelong-term reference picture which can be used from the picture in whichthe slice header is referred to.

Referring back to FIG. 8, the decoding of the SH long-term RPinformation will be described. A part (B) of FIG. 8 corresponds to theSH long-term RP information. The SH long-term RP information includesthe slice header only when the long-term reference picture can be usedin the target picture (long_term_ref_pic_present_flag). When one or morelong-term reference pictures are decoded with the SPS(num_long_term_ref_pics_sps>0), the number of reference pictures(num_long_term_sps) which can be referred to as the target picture amongthe long-term reference pictures decoded with the SPS is included in theSH long-term RP information. The number of long-term reference pictures(num_long_term_pics) explicitly transmitted with the slice header isincluded in the SH long-term RP information. Information (lt_idx_sps[i])indicating that the long-term reference pictures of the number of theforegoing num_long_term_sps are selected from the long-term referencepictures transmitted with the SPS is further included in the SHlong-term RP information. As the information regarding the long-termreference picture explicitly included in the slice header, the POCs(poc_lsb_lt[i]) of the reference pictures and the presence or absence ofpossibility to be used as the reference pictures of the target pictures(used_by_curr_pic_lt_flag[i]) are included as the number of theforegoing num_long_term_pics.

(RPL Modification Information Decoding Process)

The RPL modification information is information which is decoded fromthe SPS or the slice header to construct the reference picture list RPL.The RPL modification information includes SPS list modificationinformation and SH list modification information.

(SPS List Modification Information)

The SPS list modification information is information that is included inthe SPS and is information related to constraints of reference picturelist modifications. Referring back to FIG. 6, the SPS list modificationinformation will be described. A part (C) of FIG. 6 corresponds to theSPS list modification information. The SPS list modification informationincludes a flag restricted_ref_pic_lists_flag) indicating whether thereference picture list is common to a previous slice included in thepicture and a flag (lists_modification_present_flag) indicating whetherinformation regarding list sorting is present within the slice header.

(SH List Modification Information)

The SH list modification information is information that is included inthe slice header and includes update information of the length(reference list length) of the reference picture list applied to thetarget picture and sorting information (reference list sortinginformation) of the reference picture lists. The SH list modificationinformation will be described with reference to FIG. 9. FIG. 9exemplifies a part of the slice header syntax table that is used at thetime of the decoding of the slice header in the header informationdecoding section 10 and the reference picture information decodingsection 13. A part (C) of FIG. 9 corresponds to the SH list modificationinformation.

A flag (num_ref_idx_active_override_flag) indicating whether to update alist length is included as reference list length update information.Information (num_ref_idx_10_active_minus1) indicating the reference listlength after modification of the L0 reference list and information(num_ref_idx_11_active_minus1) indicating the reference list lengthafter modification of the L1 reference list are further included.

Information included as the reference list sorting information in theslice header will be described with reference to FIG. 10. FIG. 10exemplifies a syntax table of the reference list sorting informationused at the time of the decoding of the slice header in the headerinformation decoding section 10 and the reference picture informationdecoding section 13.

The reference list sorting information includes an L0 reference listsorting presence or absence flag (ref_pic_list_modification_flag_10).The L0 reference list sorting presence or absence flag is a referencepicture list sorting presence or absence flag related to the L0reference list. When the value of this flag is 1 (the L0 reference listis sorted) and NumPocTotalCurr is greater than 2, an L0 reference listsorting order (list_entry_10[i]) is included in the reference listsorting information. Here, NumPocTotalCurr is a variable indicating thenumber of reference pictures which can be used for a current picture.Accordingly, when the L0 reference list is sorted and the number ofreference pictures which can be used for the current picture is greaterthan 2, the L0 reference list sorting order is included in the sliceheader.

Likewise, when the reference picture is a B slice, that is, the L1reference list can be used for the target picture, an L1 reference listsorting presence or absence flag (ref_pic_list_modification_flag_11) isincluded in the reference list sorting information. The L1 referencelist sorting presence or absence flag is a reference picture listsorting presence or absence flag related to the L1 reference list. Whenthe value of this flag is 1 and NumPocTotalCurr is greater than 2, an L1reference list sorting order (list_entry_11[i]) is included in thereference list sorting information. In other words, only when the L1reference is sorted and the number of reference pictures which can beused for the current picture is greater than 2, the L1 reference listsorting order is included in the slice header.

(Details of Reference Picture Set Derivation Process)

The details of the process of S15 in the above-described moving imagedecoding order, that is, the reference picture set derivation processperformed by the reference picture set setting section, will bedescribed.

As described above, the reference picture set setting section 14generates the reference picture set RPS used for the decoding of thetarget picture based on the RPS information and the information recordedon the decoded picture buffer 12.

The reference picture set RPS is a set of pictures (referable pictures)which can be used as the reference images at the time of decoding in thetarget picture and a picture subsequent to the target picture in thedecoding order. The reference picture set can be classified into thefollowing two subsets according to the kinds of referable pictures:

-   -   a current picture referable list ListCurr: a list of the        referable pictures in the target picture among the pictures on        the decoded image buffer; and    -   a subsequent picture referable list ListFoll: a list of pictures        which are not referred to in the target picture and can be        referred to in the picture subsequent to the target picture in        the decoding order on the decoded image buffer.

The number of pictures included in the current picture referable list isreferred to as the number of current picture referable picturesNumCurrList. The above-described NumPocTotalCurr described withreference to FIG. 10 is the same as NumCurrList.

The current picture referable list is configured to include threepartial lists:

-   -   a current picture long-term referable list ListLtCurr:    -   a current picture referable picture designated by the SPS        long-term RP information or the SH long-term RP information;    -   a current picture short-term front referable list        ListStCurrBefore: a current picture referable picture designated        by the SPS short-term RPS information or the SH short-term RPS        information and earlier than the target picture in the display        order; and    -   a current picture short-term rear referable list        ListStCurrAfter: a current picture referable picture designated        by the SPS short-term RPS information or the SH short-term RPS        information and earlier than the target picture in the display        order.

The subsequent picture referable list is configured to include twopartial lists:

-   -   a subsequent picture long-term referable list ListLtFoll: a        subsequent picture referable picture designated by the SPS        long-term RP information or the SH long-term RP information; and    -   a subsequent picture short-term referable list ListStFoll: a        current picture referable picture designated by the SPS        short-term RPS information or the SH short-term RPS information.

The reference picture set setting section 14 generates the referencepicture set RPS, that is, the current picture short-term front referablelist ListStCurBefore, the current picture short-term rear referable listListStCurrAfter, the current picture long-term referable listListLtCurr, the subsequent picture short-term referable list ListStFoll,and the subsequent picture long-term referable list ListLtFoll in thefollowing order. The variable NumPocTotalCurr indicating the number ofcurrent picture referable pictures is further derived. Each of thereferable lists is assumed to be null before the following processesstart.

(S201) The single short-term reference picture set used to decode thetarget picture is specified based on the SPS short-term RPS informationand the SH short-term RPS information. Specifically, when the value ofshort_term_ref_pic_set_sps included in the SH short-term RPS informationis 0, the short-term RPS explicitly transmitted with the slice headerincluded in the SH short-term RPS information is selected. In theotherwise case (when the value of short_term_ref_pic_set_sps is 1, theshort-term RPS indicated by short_term_ref_pic_set_idx included in theSH short-term RPS information is selected from the plurality ofshort-term RPSs included in the SPS short-term RPS information.

(S202) The value of the POC of each reference picture included in theselected short-term RPS is derived, and the position of the localdecoded image recorded in association with the POC value on the decodedimage buffer 12 is detected and is derived as a recording position ofthe reference picture on the decoded image buffer.

When the reference picture is the front short-term reference picture,the value of the POC of the reference picture is derived by subtractingthe value of “delta_poc_s0_minus1[i]+1” from the value of the POC of thetarget picture. On the other hand, when the reference picture is thesubsequent short-term reference picture, the value of the POC of thereference picture is derived by adding the value of“deltapoc_s1_minus1[i]+1” to the value of the POC of the target picture.

(S203) The order in which the front reference pictures included in theshort-term RPS is transmitted is confirmed and the front referencepictures are added to the current picture short-term front referablelist ListStCurBefore when the value of the associatedused_by_curr_pic_s0_flag[i] is 1. In the otherwise case (when the valueof used_by_curr_pic_s0_flag[i] is 0), the front reference pictures areadded to the subsequent picture short-term referable list ListStFoll.

(S204) The order in which the rear reference pictures included in theshort-term RPS are transmitted is confirmed and the subsequent referencepictures are added to the current picture short-term rear referable listListStCurrAfter when the value of the associatedused_by_curr_pic_s1_flag[i] is 1. In the otherwise case (when the valueof used_by_curr_pic_s1_flag[i] is 0), the front reference pictures areadded to the subsequent picture short-term referable list ListStFoll.

(S205) The short-term reference picture set used to decode the targetpicture is specified based on the SPS long-term RP information and theSH long-term RP information. Specifically, the reference pictures of thenumber of num_long_term_sps are selected from the reference picturesincluded in the SPS long-term RP information and are added to thelong-term reference picture set in order. The selected referencepictures are the reference pictures indicated by lt_idx_sps[i].Subsequently, the reference pictures of the number of num_long_term_picsand the reference pictures included in the SH long-term RP informationare added to the long-term reference picture set in order.

(S206) The value of the POC of each reference picture included in thelong-term reference picture set is derived, and the position of thelocal decoded image recorded in association with the POC value on thedecoded image buffer 12 is detected and is derived as a recordingposition of the reference picture on the decoded image buffer.

The POC of the long-term picture is directly derived from the value ofthe associatively decoded poc_lst_lt[i] or lt_ref_pic_poc_lst_sps[i].

(S207) The reference pictures included in the long-term referencepicture set are confirmed in order and the long-term reference picturesare added to the current picture long-term referable list ListLtCurrwhen the value of the associated used_by_curr_pic_lt_flag[i] orused_by_curr_lt_sps_flag[i] is 1. In the otherwise case (when the valueof used_by_curr_pic_lt_flag[i] or used_by_curr_pic_lt_sps_flag[i] is 0),the long-term reference pictures are added to the subsequent picturelong-term referable list ListLtFoll.

(S208) The value of the variable NumPocTotalCurr is set as the a sum ofthe current picture to the referable reference picture. That is, thevalue of the variable NumPocTotalCurr is set as the sum of the number ofelements of three lists, the current picture short-term front referablelist ListStCurrBefore, the current picture short-term rear referablelist ListStCurrAfter, and the current picture long-term referable listListLtCurr.

(Details of Reference Picture List Construction Process)

The details of the process of S16 in the decoding order, that is, thereference picture list construction process, will be described withreference to FIG. 1. As described above, the reference picture listderivation section 15 generates the reference picture list RPL based onthe reference picture set RPS and RPL modification information.

The reference picture list is configured to include two lists, an L0reference list and an L1 reference list. First, a construction order ofthe L0 reference list will be described. The L0 reference list isconstructed in the order indicated in S301 to S307 below.

(S301) The provisional L0 reference list is generated and is initializedto a null list.

(S302) The reference pictures included in the current picture short-termfront referable list are added in order to the provisional L0 referencelist.

(S303) The reference pictures included in the current picture short-termrear referable list are added in order to the provisional L0 referencelist.

(S304) The reference pictures included in the current picture long-termreferable list are added in order to the provisional L0 reference list.

(S305) When the reference picture list is modified (the value oflists_modification_present_flag included in the RPL modificationinformation is 1), the following processes of S306 a to S306 b areperformed. Otherwise (the value of lists_modification_present_flag is0), the process of S307 is performed.

(S306 a) When the modification of the L0 reference picture is valid(when the value of ref_pic_list_modification_flag_10 included in the RPLmodification information is 1) and a current picture referable picturenumber NumCurrList is equal to 2, S306 b is performed. Otherwise, S306 cis performed.

(S306 b) The value of the list sorting order list_entry_10[i] includedin the RPL modification information is set according to the followingexpressions. Thereafter, S306 c is performed.

-   -   list_entry_10[0]=1    -   list_entry_10[1]=0

(S306 c) The elements of the provisional L0 reference list are sortedbased on the value of the reference list sorting order list_entry_10[i]and are set to an L0 reference list. The elements RefPicList0[rIdx] ofthe L0 reference list corresponding to the reference picture index rIdxare derived according to the following expressions. Here,RefListTemp0[i] indicates an i-th element of the provisional L0reference list.RefPicList0[rIdx]=RefPicListTemp0[list_entry—10[rIdx]]

According to the above expression, in the reference list sorting orderlist_entry_10[i], the reference picture recorded at the position of theabove value in the provisional L0 reference list is stored as thereference picture at the position of rIdx in the L0 reference list withreference to the value recorded at the position indicated by thereference picture index rIdx.

(S307) The provisional L0 reference list is set as the L0 referencelist.

Next, the L1 reference list is constructed. The L1 reference list canalso be constructed in the same order as that of the L0 reference list.In the construction order (S301 to S307) of the L0 reference list, theL0 reference picture, the L0 reference list, the provisional L0reference list, list_entry_10 may be substituted with the L1 referencepicture, the L1 reference list, the provisional L1 reference list, andlist_entry_11, respectively.

(Description of Validity and Advantageous Effects of Reference ListModification)

The reference picture information decoding process and the referencepicture list construction process in the moving image decoding deviceaccording to the embodiment have been described above. Next, the factthat the reference picture can be modified and the reference picturelist modification information can be transmitted with a smaller numberof codes through such processes will be described.

<Validity of Reference List Modification>

Referring to the processes of S305 and S306 in the L0 reference listconstruction process, the provisional L0 reference list is used directlyas the L0 reference list when the L0 reference list is not modified.From this viewpoint, the provisional L0 reference list is a standard(default) L0 reference list used when the sorting is not performed. Inthis sense, the provisional L0 reference list can also be referred to asthe standard L0 reference list.

When the meaning of the list sorting list is confirmed again, the valueof list_entry_10[0] is a value indicating at which element the 0-thelement of the L0 reference list after the sorting is located in thestandard L0 reference list. In general, the value of list_entry_10[i] isa value indicating at which element an i-th element of the L0 referencelist after the sorting is located in the standard L0 reference list.

In the process of S306 a, the value of list_entry_10[0] is set to 1 andthe value of list_entry_10[1] is set to 0 when the modification of theL0 reference list is effective and the value of NumCurrList is 2. Inother words, the reference lists are sorted so that the first element ofthe standard L0 reference list becomes the zeroth element of the L0reference list and the zeroth element of the standard L0 reference listbecomes the first element of the L0 reference list. Here, the number ofelements of the L0 reference list is equal to or less than the number ofcurrent picture referable pictures (equal to or less than the value ofNumCurrList). Accordingly, when the value of NumCurrList is 2, thenumber of elements of the L0 reference list is equal to or less than 2.Therefore, the L0 reference list sorting information used to sort the L0reference list is only the first element (list_entry_10[0]) and thesecond element (list_entry_10[1]) of list_entry10 and the elementssubsequent to the third element are not used. In this case, in thesorting of the reference lists, a combination of (list_entry_10[0] andlist entry10[1]) is either O1 or O2 below.(L0List[0],L0List[1])=(TmpList[0],TmpList[1])  O1(L0List[0],L0List[1])=(TmpList[1],TmpList[0])  O2

When the number of current picture referable pictures is 2 and the L0reference list is not modified in the above-described reference picturelist modification process, the L0 reference list of the foregoing O1 isused. On the other hand, when the L0 reference list is modified, the L0reference list of the foregoing O2 is used. Accordingly, when the numberof current picture referable pictures is 2 in the reference picture listmodification process, all of the possible sortings of the L0 referencelist can be selected.

<Coding Amount of Reference List Modification Information>

In S306 a in the L0 reference list construction process, the value oflist_entry_10[i] is set directly without using information (that is, asyntax value decoded in the slice header) included in the PRLmodification information when the modification of the L0 reference listis effective and the value of NumCurrList is 2. The elements subsequentto the third element (list_entry_10[i] (where i>1)) of the list_entry_10have not been used. Accordingly, when the modification of the L0reference list is effective and the value of NumCurrList is 2, it is notnecessary to decode the syntax information of list_entry_10 in the sliceheader. Actually, it has been described that the transmission oflist_entry_10[i] is omitted in the decoding process for the RPLmodification information described with reference to FIG. 10 when themodification of the L0 reference picture is effective and the value ofNumCurrList is 2 (when NumPocTotalCurr is 2). In other words, when thenumber of current picture referable pictures satisfies a specificcondition (when this number is 2), a coding amount related to thetransmission of the RPS information is reduced and a coding amount ofthe slice header is accordingly reduced by omitting signaling of the RPLsorting information.

As described above, in the moving image decoding device according to theembodiment, the reference picture information decoding section omits thedecoding of the reference picture sorting information when the number ofcurrent picture referable pictures is 2. When the number of currentpicture referable pictures is 2 and it is necessary to modify thereference list, the reference picture setting section sets the referencepicture sorting order such that the first element of the standardreference list becomes the zeroth element and the zeroth element of thestandard reference list becomes the first element of the reference list.In this way, the moving image decoding device according to theembodiment reduces the coding amount related to the reference listinformation while maintaining the function of modifying the referencepicture list.

MODIFICATION EXAMPLE 1 Omission of RPL Modification Information whenNumber of Current Picture Referable Pictures is 1

In the first embodiment, the example in which the RPL modificationinformation is omitted when the number of current picture referablepictures is 2 has been described, but the present invention is notlimited thereto. When the number of current picture referable picturesis 1, the RPL modification information may be omitted.

Specifically, in the decoding process for the SH list modificationinformation in the reference picture information decoding section 13,the reference list sorting information is parsed based on the syntaxtable illustrated in FIG. 11. FIG. 11 exemplifies the syntax table ofthe reference list sorting information used at the time of the decodingof the slice header.

The L0 reference list sorting presence or absence flag(ref_pic_list_modification_flag_10), the L1 reference list sortingpresence or absence flag (ref_pic_list_modification_flag_11), the L0reference list sorting order (list_entry_10[i]), and the L1 referencelist sorting order_list_entry_11[i]) included in the reference listsorting information are decoded only when the number of current picturereferable pictures is greater than 1. That is, when the number ofcurrent picture referable pictures is 1, the reference list sortinginformation is not decoded.

When the number of current picture referable pictures is 1, the listlength of the reference list is 1 at most, and thus it is not necessaryto sort the reference picture list. Accordingly, when the number ofcurrent picture referable pictures is 1, it is possible to reduce thecoding amount of the slice header by omitting the decoding of thereference picture list sorting presence or absence flag and/or thereference list sorting order.

The example in which the reference list sorting information issubstituted with the syntax table illustrated in FIG. 11 has beendescribed. However, the syntax table in FIG. 10 is used as the syntaxtable of the reference list sorting information, and then a syntax tableillustrated in FIG. 12 may be used to decode the slice header. In thesyntax table of the slice header illustrated in FIG. 12, the referencelist sorting information (ref_pic_list_modification( )) is decoded onlywhen the number of current picture referable pictures (NumPocTotalCurr)is greater than 1.

MODIFICATION EXAMPLE 2 Transmission of NumPocTotalCurr

In Modification Example 1 described above, the example in which thevalue of the variable NumPocTotalCurr derived based on the RPSinformation is used as the number of current picture referable pictureshas been described, but the present invention is not limited thereto.For example, information corresponding to the number of current picturereferable picture may be decoded directly from the coded data to beused.

Specifically, in the decoding process for the SH list modificationinformation in the reference picture information decoding section 13,the reference list sorting information is parsed based on a syntax tableillustrated in FIG. 13. FIG. 13 exemplifies the syntax table of thereference list sorting information used at the time of the decoding ofthe slice header. A difference from the syntax table described in FIG.10 is that a syntax value num_poc_total_curr is first decoded. Here,num_poc_total_curr is decoded by, for example, a code with a fixedlength of 4 bits. The code length of num_poc_total_curr is notnecessarily 4 bits. However, when the upper limit of the number ofcurrent picture referable pictures is 16, it is preferable to use thefixed length of 4 bits. Unlike the case of FIG. 10, the value of thesyntax num_poc_total_curr is used to determine whether the value of thenumber of current picture referable pictures is greater than 2 in thedetermination of whether list_entry_10 or list_entry11 is transmitted.

According to the foregoing modification example, it is necessary to addthe decoding of the syntax num_poc_total_curr. However, it is notnecessary to use the information regarding NumPocTotalCurr derived basedon the RPS information at the time of the decoding of the referencepicture list modification information (ref_pic_list_modification).Therefore, the slice header including the reference picture listmodification information can be parsed with a smaller processing amount.Since the RPS information is included in not only the slice but also theSPS, it is possible to reduce the dependency on the SPS in the parsingof the slice header. In this way, it is possible to obtain theadvantageous effect of improving error resistance.

In the foregoing modification example, the example in which thedetermination according to the number of current picture referablepictures is included directly in the determination expression of thesyntax table has been described, but the direct decoding of the syntaxnum_poc_total_curr is effective even in the other cases. For example,the direct decoding of the syntax num_poc_total_curr is effective evenwhen the syntax element list_entry_10[i] is coded by a code with avariable length based on the number of current picture referablepictures.

As another specific example, the reference list sorting information maybe parsed based on the syntax table illustrated in FIG. 14. A differencefrom the syntax table described in FIG. 13 is that a flag indicatingwhether to modify the reference list L0 and the reference list L1 isfirst decoded and the value of the syntax num_poc_total_curr is decodedonly when one reference picture list is modified. When the flag is notdecoded, the value of num_poc_total_curr is set to 0.

When the reference list is not modified, the reference list sortinginformation can be parsed even without using the number of currentpicture referable pictures. Therefore, only when the reference list ismodified, it is possible to omit redundancy and reduce the coding amountby decoding the syntax num_poc_total_curr.

As still another example, the reference list sorting information may beparsed based on a syntax table illustrated in FIG. 15. A difference fromthe syntax table described in FIG. 13 is that a syntaxceil-log2_num_poc_total_curr is decoded instead of the decoding of thesyntax num_poc_total_curr and whether to decode the reference listsorting order is determined based on the value. A value V of the syntaxceil-log2_num_poc_total_curr can be derived according to the followingexpression when N is the number of current picture referable pictures.V=ceil(log 2(N))

Here, log 2(A) indicates a logarithm of (A) with a base 2 and ceil(A)means the largest integer value that does not exceed the value of A. Thevalue of the syntax ceil_log2_num_poc_total_curr corresponds to thenumber of digits when the number of current picture referable picturesis expressed in binary numbers.

By decoding only information necessary for the parsing in the referencelist sorting order without the direct decoding of the number of currentpicture referable pictures, it is possible to reduce the coding amountcompared to the case in which the coding amount of the slice header isdirectly decoded.

As still another example, the reference list sorting information may beparsed based on a syntax table illustrated in FIG. 16. A difference fromthe syntax described in FIG. 12 is that the value of a syntaxnum_poc_total_curr_greater1_flag is decoded in the beginning and whetherto decode the reference list modification presence or absence flag andthe reference list sorting order is determined based on the valueinstead of the variable NumPocTotalCurr. Here, the syntaxnum_poc_total_curr_greater1_flag indicates whether the number of currentpicture referable pictures is greater than 1. That is, when the numberof current picture referable pictures is equal to or greater than 2, thetrue is set. When the number of current picture referable pictures isequal to or less than 1, the false is set.

In this case, compared to the case in which the variable NumPocTotalCurris used, it is possible to obtain the advantageous effects of reducingthe parsing process for the slice header and improving error resistance.Further, it is possible to obtain the advantageous effect that anincrease in the coding amount of the slice header is less than in thecase in which the number of current picture referable pictures isdirectly decoded.

MODIFICATION EXAMPLE 3 Another Example of Reference Picture ListConstruction Process

The reference picture list construction process described above withreference to FIG. 1 has been described as the process assumed that thelength of the L0 reference list is equal to or less than the number ofcurrent picture referable pictures, but the present invention is notlimited thereto. For example, by directly designating the length of theL0 reference list as reference list length update information by asyntax num_refidx_10_active_minus1, the length of the L0 reference listis greater than the number of current picture referable pictures in somecases. In these cases, the reference picture list (herein, the L0reference list) can be constructed in the following order.

(S401) The value of an L0 reference list length lenL0 is set to“num_refidx_10_active minus1+1.”

(S402) A L0 referable list is generated and is initialized to a nulllist.

(S403) The reference pictures included in the current picture short-termfront referable list are added to the L0 referable list in order.

(S404) The reference pictures included in the current picture short-termrear referable list are added to the L0 referable list in order.

(S405) The reference pictures included in the current picture long-termreferable list are added to the L0 referable list in order.

(S406) when the L0 reference list is modified (when the value ofref_pic_list_modification_flag_10 is 1), S407 a is performed. In theother cases, S407 b is performed.

(S407 a) Integers within a range equal to or greater than 0 and equal toor less than (lenL0-1) are sequentially set to rIdx and the referencepicture corresponding to the element at the position of a referenceindex rIdx of the L0 reference list is set according to the followingexpression.RefPicList0[rIdx]=RpsCurrList0[list_entry—10[rIdx]]

In the foregoing expression, RefPicList0[A] indicates an element valueat the position of A of the L0 reference list. RpsCurrList0[A] indicatesan element value at a position indicated by A of the L0 referable list.The number of elements of the L0 referable list is the same as thenumber of current picture referable pictures NumPocTotalCurr and a rangeof the value of list_entry_10[rIdx] is an integer value of a range equalto or greater than 0 and less than NumPocTotalCurr.

According to the above expression, in the reference list sorting orderlist_entry_10[i], a value recorded at a position indicated by thereference picture index rIdx is referred to and the reference picturerecorded at the position of the value in the L0 referable list is storedas a reference picture at the position of rIdx of the L0 reference list.

(S407 b) Integers within a range equal to or greater than 0 and equal toor less than (lenL0-1) are sequentially set to rIdx and the referencepicture corresponding to the element at the position of a referenceindex rIdx of the L0 reference list is set according to the followingexpression.RefPicList0[rIdx]=RpsCurrList0[rIdx % NumPocTotalCurr]

According to the above expression, the reference picture associated withthe position of rIdx in the L0 reference list is a picture recorded at aposition of a remainder obtained by dividing rIdx in the L0 referablelist by the number of current picture referable pictures, that is, aremainder obtained by dividing the reference image index by the lengthof the L0 reference list.

In other words, the reference picture list is set with reference to theelements of the referable list (the L0 referable list) generated bysorting the current picture referable pictures in a given priorityorder. In the generation of the L0 reference list (basic L0 referencelist) when the L0 reference list is not modified in S407 b, thereference is made by the remaining value obtained by dividing the valuethe reference index rIdx by the number of current picture referablepictures.

In the foregoing example, the number of elements of the L0 referablelist RpsCurrList0 has been set to NumPocTotalCurr, but the length of thereferable list can also be set to L0 reference list length LenL0instead. However, since the L0 referable list can be generated withoutdependency on the length of the reference list likely to be updated inthe slice unit, it is preferable to set the number of elements of the L0referable list RpsCurrList0 to NumPocTotalCurr.

By constructing the L0 reference list in the foregoing order, it ispossible to construct the L0 reference list even when the length of theL0 reference list increases from the number of current picture referablepictures.

The L0 reference list has been described above, but the same descriptionis also established in the L1 reference list.

[Moving Image Coding Device]

Hereinafter, the moving image coding device 2 according to theembodiment will be described with reference to FIG. 17.

(Overview of Moving Image Coding Device)

Roughly speaking, the moving image coding device 2 is a device thatgenerates coded data #1 by coding input image #10 and outputs the codeddata #1.

(Configuration of Moving Image Coding Device)

First, a configuration example of the moving image coding device 2 willbe described with reference to FIG. 17. FIG. 17 is a functional blockdiagram illustrating the configuration of the moving image coding device2. As illustrated in FIG. 17, the moving image coding device 2 includesa picture decoding section 11, a decoded picture buffer 12, a headercoding section 20, a picture coding section 21, a reference picture setdecision section 24, and a reference picture list decision section 25.The header coding section 20 includes a reference picture informationcoding section 23 therein. The picture decoding section 11 and thedecoded picture buffer 12 are the same as the constituent elements withthe same names described in FIG. 2, and thus the description thereofwill be omitted.

The header coding section 20 generates and codes the SPS, the PPS, andthe slice header based on the input image #10 and outputs the SPS, thePPS, and the slice header.

The reference picture information coding section 23 is included in theheader coding unit 16. The reference picture information coding section23 performs a reference picture information coding process based on thereference picture set RPS and the reference picture list RPL to generatethe RPS information and the RPL modification information included in theSPS and the slice header.

The picture coding section 21 codes each picture based on the inputimage #10 and the reference picture list RPL and outputs each picture.

The reference picture set decision section 24 decides and outputs thereference picture set RPS used in the coding and the local decoding ofthe coding target picture based on the input image #10 and the localdecoded image recorded on the decoded picture buffer 12.

The reference picture list decision section 25 decides and outputs thereference picture list RPL used in the coding and the local decoding ofthe coding target picture based on the input image #10 and the referencepicture set.

(Correspondence Relation with Moving Image Decoding Device)

The moving image coding device 2 has the configuration corresponding toeach configuration of the moving image decoding device 1. Here, thecorrespondence means a relation in which the same process or its reverseprocess is performed.

For example, the reference picture information decoding process of thereference picture information decoding section 13 included in the movingimage decoding device 1 is the same as the reference picture informationcoding process of the reference picture information coding section 23included in the moving image coding device 2. More specifically, thereference picture information decoding section 13 generates the RPSinformation and the modification RPL information as the syntax valuedecoded from the SPS or the slice header. On the other hand, thereference picture information coding section 23 codes the input RPSinformation and modification RPL information as the syntax values of theSPS and the slice header.

For example, in the moving image decoding device 1, a process ofdecoding the syntax value from a bit string corresponds to a process ofcoding the bit string from the syntax value and its reverse process inthe moving image coding device 2.

(Flow of Process)

An order in which the moving image coding device 2 generates the outputcoded data #1 from the input image #10 is as follows.

(S21) The following processes of S22 to S29 are performed on eachpicture (target picture) configuring the input image #10.

(S22) The reference picture set decision section 24 decides the targetpicture in the input image #10 and the reference picture set RPS basedon the local decoded image recorded on the decoded picture buffer 12 andoutputs the target picture and the reference picture set RPS to thereference picture list decision section 25. The RPS informationnecessary to generate the reference picture set RPS is derived andoutput to the reference picture information coding section 23.

(S23) The reference picture list decision section 25 derives thereference picture list RPL based on the target picture in the inputimage #10 and the input reference picture set RPS and outputs thereference picture list RPL to the picture coding section 21 and thepicture decoding section 11. The RPL modification information necessaryto generate the reference picture list RPL is derived and output to thereference picture information coding section 23.

(S24) The reference picture information coding section 23 generates theRPS information and the RPL modification information to be included inthe SPS or the slice header based on the reference picture set RPS andthe reference picture list RPL.

(S25) The header coding section 20 generates the SPS to be applied tothe target picture based on the input image #10 and the RPS informationand the RPL modification information generated by the reference picturecoding section 21 and outputs the SPS.

(S26) The header coding section 20 generates the PPS to be applied tothe target picture based on the input image #10 and outputs the PPS.

(S27) The header coding section 20 codes the slice header of each sliceconfiguring the target picture based on the input image #10 and the RPSinformation and the RPL modification information generated by thereference picture coding section 21, outputs the slice header as a partof the coded data #1 to the outside, and outputs the slice header to thepicture decoding section 11.

(S28) The reference picture coding section 21 generates the slice dataof each slice configuring the target picture based on the input image#10, outputs the slice data as a part of the coded data #1 to theoutside, and outputs the slice data to the picture decoding section 11.

(S29) The picture decoding section 11 generates the local decoded imageof the target picture from the coded data #1 based on the slice data ofeach slice included in the target picture and the reference picture listRPL and records the local decoded image on the decoded picture buffer inassociation with the POC of the target picture.

Application Examples

The moving image coding device 2 and the moving image decoding device 1described above can be mounted to be used in various apparatusestransmitting, receiving, recording, and reproducing a moving image. Themoving image may be a natural moving image captured by a camera or thelike or may be an artificial moving image (including a CG and a GUI)generated by a computer or the like.

First, the fact that the moving image coding device 2 and the movingimage decoding device 1 described above can be used to transmit andreceive a moving image will be described with reference to FIG. 18.

(a) of FIG. 18 is a block diagram illustrating the configuration of atransmission apparatus PROD_A on which the moving image coding device 2is mounted. As illustrated in (a) of FIG. 18, the transmission apparatusPROD_A includes a coding section PROD_A1 that obtains coded data bycoding a moving image, a modulation section PROD_A2 that obtains amodulated signal by modulating a carrier wave with the coded dataobtained by the coding section PROD_A1, and a transmission sectionPROD_A3 that transmits the modulated signal obtained by the modulationsection PROD_A2. The above-described moving image coding device 2 isused as the coding section PROD_A1.

The transmission apparatus PROD_A may further include a camera PRODA4that captures a moving image as a supply source of a moving image inputto the coding section PROD_A1, a recording medium PROD_A5 that recordsthe moving image, an input terminal PROD_A6 that inputs the moving imagefrom the outside, and an image processing section A7 that generates orprocesses an image. In (a) of FIG. 18, the configuration of thetransmission apparatus PROD_A including all of the sections isexemplified, but some of the sections may be omitted.

The recording medium PROD_A5 may be a recording medium that records anuncoded moving image or may be a recording medium that records a movingimage coded according to a coding scheme for recording different from acoding scheme for transmission. In the latter case, a decoding section(not illustrated) that decodes coded data read from the recoding mediumPROD_A5 according to the coding scheme for recording may be interposedbetween the recording medium PROD_A5 and the coding section PROD_A1.

(b) of FIG. 18 is a block diagram illustrating a reception apparatusPROD_B on which the moving image decoding device 1 is mounted. Asillustrated in (b) of FIG. 18, the reception apparatus PROD_B includes areception section PROD_B1 that receives a modulated signal, ademodulation section PROD_B2 that obtains coded data by demodulating themodulated signal received by the reception section PROD_B1, and adecoding section PROD_B3 that obtains a moving image by decoding thecoded data obtained by the demodulation section PROD_B2. Theabove-described moving image decoding device 1 is used as the decodingsection PROD_B3.

The reception apparatus PROD_B may further include a display PROD_B4that displays the moving image as a supply destination of the movingimage output by the decoding section PROD_B3 a recording medium PROD_B5that records the moving image, and an output terminal PROD_B6 thatoutputs the moving image to the outside. In (b) of FIG. 18, theconfiguration of the reception device PROD_B including all of thesesections is exemplified, but some of the sections may be omitted.

The recording medium PROD_B5 may be a recording medium that records anuncoded moving image or may be a recording medium that records a movingimage coded according to a coding scheme for recording different from acoding scheme for transmission. In the latter case, a coding section(not illustrated) that codes the moving image acquired from the decodingsection PROD_B3 according to the coding scheme for recording may beinterposed between the decoding section PROD_B3 and the recording mediumPROD_B5.

A transmission medium through which a modulated signal is transmittedmay be a wireless medium or a wired medium. A transmission form in whicha modulated signal is transmitted may be broadcasting (here, atransmission form in which a transmission designation is not specifiedin advance) or may be communication (here, a transmission form in whicha transmission destination is specified in advance). That is, thetransmission of the modulated signal may be realized by any one ofwireless broadcasting, wired broadcasting, wireless communication, andwired communication.

For example, a broadcast station (broadcast equipment or thelike)/reception station (a television receiver or the like) forterrestrial digital broadcasting is an example of the transmissionapparatus PROD_A/reception apparatus PROD_B transmitting or receiving amodulated signal by wireless broadcasting. Further, a broadcast station(broadcast equipment or the like)/reception station (television receiveror the like) for cable television broadcasting is an example of thetransmission apparatus PROD_A/reception apparatus PROD_B transmitting orreceiving a modulated signal by wired broadcasting.

A server (a workstation or the like)/client (a television receiver, apersonal computer, a smartphone, or the like) for a Video On Demand(VOD) service in which the Internet is used, a moving image sharingservice, or the like is an example of the transmission apparatusPROD_A/reception apparatus PROD_B transmitting or receiving a modulatedsignal by communication (typically, one of wireless and wired media isused as a transmission medium in a LAN and a wired medium is used as atransmission medium in a WAN). Here, the personal computer includes adesktop PC, a laptop PC, and a tablet PC. The smartphone also includes amulti-function portable phone terminal.

The client for the moving image sharing service has not only a functionof decoding coded data downloaded from the server and displays the codeddata on a display but also a function of coding a moving image capturedby a camera and uploading the coded moving image to the server. That is,the client for the moving image sharing service functions as both of thetransmission apparatus PROD__A and the reception apparatus PROD_B.

Next, the fact that the moving image coding device 2 and the movingimage decoding device 1 described above can be used to record andreproduce a moving image will be described with reference to FIG. 19.

(a) of FIG. 19 is a block diagram illustrating the configuration of arecording apparatus PROD_C on which the above-described moving imagecoding device 2 is mounted. As illustrated in (a) of FIG. 19, therecording apparatus PROD_C includes a coding section PROD_C1 thatobtains coded data by coding a moving image and a writing sectionPROD_C2 that writes the coded data obtained by the coding sectionPROD_C1 on a recording medium PROD_M. The above-described moving imagecoding device 2 is used as the coding section PROD_C1.

The recording medium PROD_M may be (1) a type of medium that is includedin the recording apparatus PROD_C, such as a hard disk drive (HDD) or asolid state drive (SSD), may be (2) a type of medium that is connectedto the recording apparatus PROD_C, such as an SD memory card or aUniversal Serial Bus (USB) flash memory, or may be (3) a medium that isloaded on a drive device (not illustrated) included in the recordingapparatus PROD_C, such as a Digital Versatile Disc (DVD) or a Blu-ray(registered trademark) disc (BD).

The recording apparatus PROD_C may further include a camera PROD_C3 thatcaptures a moving image as a supply source of a moving image to be inputto the coding section PROD_C1, an input terminal PROD_C4 that inputs amoving image from the outside, a reception section PROD_C5 that receivesa moving image, and an image processing section C6 that generates orprocesses an image. In (a) of FIG. 19, the configuration of therecording apparatus PROD_C including all of the sections is exemplified,but some of the sections may be omitted.

The reception section PROD_C5 may be a reception section that receivesan uncoded moving image or may be a reception section that receivescoded data coded according to a coding scheme for transmission differentfrom a coding scheme for recording. In the latter case, a decodingsection (not illustrated) for transmission that decodes the coded datacoded according to the coding scheme for transmission may be interposedbetween the reception section PROD_C5 and the coding section PROD_C1.

As the recording apparatus PROD_C, for example, a DVD recorder, a BDrecorder, and a Hard Disk Drive (HDD) recorder can be exemplified (inthis case, the input terminal PROD_C4 or the reception PROD_C5 is a mainsupply source of a moving image). A camcorder (in this case, the cameraPROD_C3 is a main supply source of a moving image), a personal computer(in this case, the reception section PROD_C5 or the image processingsection C6 is a main supply source of a moving image), a smartphone (inthis case, the camera PROD_C3 or the reception section PROD_C5 serves amain supply source of a moving image), and the like are also examples ofthe recording apparatus PROD_C.

(b) of FIG. 19 is a block diagram illustrating the configuration of areproduction apparatus PROD_D on which the above-described moving imagedecoding device 1 is mounted. As illustrated in (b) of FIG. 19, thereproduction apparatus PROD_D includes a reading section PROD_D1 thatreads coded data written on a recording medium PROD_M and a decodingsection PROD_D2 that obtains a moving image by decoding the coded dataread by the reading section PROD_D1. The above-described moving imagedecoding device 1 is used as the decoding section PROD_D2.

The recording medium PROD_M may be (1) a type of medium that is includedin the reproduction apparatus PROD_D, such as an HDD or an SSD, may be(2) a type of medium that is connected to the reproduction apparatusPROD_D, such as an SD memory card or a USB flash memory, or may be (3) amedium that is loaded on a drive device (not illustrated) included inthe reproduction apparatus PROD_D, such as a DVD or a BD.

The reproduction apparatus PROD_D may further includes a display PROD_D3that displays a moving image as a supply destination of the moving imageoutput by the decoding section PROD_D2, an output terminal PROD_C4 thatoutputs the moving image to the outside, and a transmission sectionPROD_D5 that transmits the moving image. In (b) of FIG. 19, theconfiguration of the reproduction apparatus PROD_D including all of thesections is exemplified, but some of the sections may be omitted.

The transmission section PROD_D5 may be a transmission section thattransmits an uncoded moving image or may be a transmission section thattransmits the coded data coded according to a coding scheme fortransmission different from a coding scheme for recording. In the lattercase, a coding section (not illustrated) that codes a moving imageaccording to the coding scheme for transmission may be interposedbetween the decoding section PROD_D2 and the transmission sectionPROD_D5.

As the reproduction apparatus PROD_D, for example, a DVD player, a BDplayer, and an HDD player can be exemplified (in this case, the outputterminal PROD_D4 connected to a television receiver or the like is amain supply destination of a moving image). A television receiver (inthis case, the display PROD_D3 is a main supply destination of a movingimage), a digital signage (which is also referred to as an electronicsignboard or an electronic bulletin board and the display PROD_D3 or thetransmission section PROD_D5 is a main supply destination of a movingimage), a desktop PC (in this case, the output terminal PROD_D4 or thetransmission section PROD_D5 is a main supply destination of a movingimage), a laptop or tablet PC (in this case, the display PROD_D3 or thetransmission section PROD_D5 is a main supply destination of a movingimage), a smartphone (in this case, the display PROD_D3 or thetransmission section PROD_D5 is a main supply destination of a movingimage), and the like are examples of the reproduction apparatus PROD_D.

Conclusion

As described above, according to an aspect of the present invention,there is provided an image decoding device generating a predicted imagethrough motion compensation prediction with reference to one or morereference images recorded on a decoded picture buffer and using thepredicted image in image decoding. The image decoding device includes:reference picture set derivation means for deriving a reference pictureset to be applied to a target picture; reference picture list generationmeans for generating a reference picture list available in the targetpicture based on reference picture list (RPL) modification informationdecoded from a slice header and the reference picture set derived by thereference picture set derivation means; and reference pictureinformation decoding means for omitting decoding of a part ofinformation included in the RPL modification information based on thenumber of current picture referable pictures.

The RPL modification information may include at least a referencepicture list sorting presence or absence flag and a reference listsorting order. The reference picture information decoding means may omitthe decoding of at least one of the reference picture list sortingpresence or absence flag and the reference list sorting order based onthe number of current picture referable pictures.

The reference picture information decoding means may omit the decodingof the reference picture list sorting presence or absence flag and thereference list sorting order when the number of current picturereferable pictures is 1.

The number of current picture referable pictures may be decoded by thereference picture information decoding means.

According to another aspect of the present invention, there is providedan image decoding device generating a predicted image through motioncompensation prediction with reference to one or more reference imagesrecorded on a decoded picture buffer and using the predicted image inimage decoding. The image decoding device includes: reference pictureset derivation means for deriving a reference picture set to be appliedto a target picture based on reference picture set (RPS) informationdecoded from a sequence parameter set (SPS) or a slice header; referencepicture list generation means for generating a reference picture listavailable in the target picture based on reference picture list (RPL)modification information decoded from the SPS or the slice header andthe reference picture set derived by the reference picture setderivation means; and reference picture information decoding means foromitting decoding of at least one of a reference list sorting presenceor absence flag (also referred to as a reference picture list sortingpresence or absence flag) and a reference list sorting order based onthe number of current picture referable pictures.

In the foregoing configuration, the decoding of at least one of thereference list sorting presence or absence flag and the reference listsorting order is omitted based on the number of current picturereferable pictures. Accordingly, it is possible to prevent informationregarding the reference picture unnecessary in the decoding from beingtransmitted, and thus it is possible to decode a moving image with aheader information of a smaller coding amount.

In the image decoding device according to the present invention, thereference picture information decoding means may omit the decoding ofthe reference list sorting order when the number of current picturereferable pictures is 2. The reference picture list generation means maygenerate a reference picture list of the reference list sorting orderwhich is an order in which an order of elements of the reference picturelist after sorting is different from a standard reference picture listwhen the number of current picture referable pictures is 2.

In the foregoing configuration, when the number of current picturereferable pictures is 2, it is possible to select the proper referencepicture list, and thus it is possible to decode a moving image using theproper reference picture list.

In the image decoding device according to the aspect of the presentinvention, the reference picture information decoding means may omit thedecoding of the reference list sorting presence or absence flag and thereference list sorting order when the number of current picturereferable pictures is 1.

When the number of current picture referable pictures is 1, the listlength of the reference list is 1 at most and it is not necessary tosort the reference picture list. In the foregoing configuration, whenthe number of current picture referable pictures is 1, decoding of thethe reference picture list sorting presence or absence flag and thereference list sorting order are omitted. Therefore, it is possible toreduce a coding amount of the slice header.

In the image decoding device according to the aspect of the presentinvention, the number of current picture referable pictures may bedecoded by the reference picture information decoding means.

In the foregoing configuration, it is possible to parse the slice headerincluding the reference picture list modification information with asmall processing amount. Further, it is possible to reduce thedependency on the sequence parameter set SPS in the parsing of the sliceheader. Thus, it is possible to achieve an improvement in errorresistance.

According to still another aspect of the present invention, there isprovided an image coding device generating a predicted image throughmotion compensation prediction with reference to one or more referenceimages recorded on a decoded picture buffer and using the predictedimage in image coding. The image coding device includes: a referencepicture set decision mechanism that decides a reference picture set anda reference picture list to be applied to a target picture; and areference picture information coding mechanism that omits coding of atleast one of a reference list sorting presence or absence flag and areference list sorting order based on the number of current picturereferable pictures.

In the foregoing configuration, the coding of at least one of thereference list sorting presence or absence flag and the reference listsorting order is omitted based on the number of current picturereferable pictures. Accordingly, it is possible to prevent informationregarding the reference picture unnecessary in the decoding from beingtransmitted, and thus it is possible to generate the coded data so thata moving image is decoded with a header information of a smaller codingamount.

(Realization by Hardware and Realization by Software)

Each block of the moving image decoding device 1 and the moving imagecoding device 2 described above may be realized by hardware such as alogical circuit formed on an integrated circuit (IC chip) or may berealized by software using a central processing unit (CPU).

In the latter case, each of the foregoing devices includes a CPU thatexecutes a command of a program realizing each function, a read-onlymemory (ROM) that stores the program, a random access memory (RAM) onwhich the program is loaded, and a storage device (recording medium)such as a memory that stores the program and various kinds of data. Anobject of the present invention can also be achieved by providing eachof the foregoing devices with a recording medium that records a programcode (an execution format program, an intermediate code program, or asource program) of a control program of each of the foregoing deviceswhich is software realizing the above-described functions in acomputer-readable manner and by causing a computer (a CPU or an MPU) toread and execute the program code recorded on the recording medium.

As the recording medium, for example, a kind of tape such as a magnetictape or a cassette tape, a kind of disc including a magnetic disk suchas floppy (registered trademark) disk/hard disk and an optical disc suchas Compact Disc Read-Only Memory (CD-ROM)/Magneto-Optical Disc (MOdiscs)/Mini Disc (MD)/Digital Versatile Disc (DVD)/CD Recordable(CD-R)/Blu-ray (registered trademark) Disc, a kind of card such as an ICcard (including a memory card)/optical card, a kind of semiconductormemory such as mask ROM/Erasable Programmable Read-Only Memory(EPROM)/Electrically Erasable and Programmable Read-Only Memory (EEPROM)(registered trademark)/flash ROM, or a kind of logical circuit such as aProgrammable Logic device (PLD) or a Field Programmable Gate Array(FPGA) can be used.

Each of the foregoing devices may be configured to be connected to acommunication network and the program code may be supplied via thecommunication network. The communication network may be able to transmitthe program code and is not particularly limited. For example, theInternet, an intra-net, an extra-net, a Local Area Network (LAN), anIntegrated Services Digital Network (ISDN), a Value-Added Network (VAN),a Community Antenna television/Cable Television (CATV) communicationnetwork, a virtual private network, a telephone circuit network, amobile communication network, or a satellite communication network canbe used. A transmission medium configuring the communication network maybe a medium capable of transmitting the program code and is notparticularly limited to a specific configuration or a kind of medium.For example, a wired medium such as Institute of Electrical andElectronic Engineers (IEEE) 1394, a USB, power line broadcasting, acable TV circuit line, a telephone line, or an Asymmetric DigitalSubscriber Line (ADSL) circuit, an infrared medium such as Infrared DataAssociation (IrDA) or a remote controller, or a wireless medium such asBluetooth (registered trademark), IEEE 802.11 wireless, High Data Rate(HDR), Near Field Communication (NFC), Digital Living Network Alliance(DLNA) (registered trademark), a portable telephone network, a satellitecircuit, or a terrestrial digital network can be used. The presentinvention can also be realized in a form of a computer data signal inwhich the program code is embodied through electronic transmission andis embedded in a carrier wave.

The present invention is not limited to the above-described embodiments,but may be modified in various forms within the scope indicated by theclaims. That is, embodiments obtained by combining technical mechanismsproperly changed within the scope indicated by the claims are includedin the technical scope of the present invention. By combining technicalmechanisms disclosed in the respective embodiments, it is possible toachieve new technical features.

INDUSTRIAL APPLICABILITY

The present invention can be properly applied to an image decodingdevice decoding coded data coded from image data and an image codingdevice generating the coded data coded from the image data. Further, thepresent invention can be properly applied to a data structure of codeddata generated by the image coding device and referred to by the imagedecoding device.

REFERENCE SIGNS LIST

1 MOVING IMAGE DECODING DEVICE (IMAGE DECODING DEVICE)

2 MOVING IMAGE CODING DEVICE (IMAGE CODING DEVICE)

10 HEADER DECODING SECTION

11 PICTURE DECODING SECTION

12 DECODED PICTURE BUFFER

13 REFERENCE PICTURE INFORMATION DECODING SECTION (REFERENCE PICTUREINFORMATION DECODING MEANS)

14 REFERENCE PICTURE SET SETTING SECTION (REFERENCE PICTURE SETDERIVATION MEANS)

15 REFERENCE PICTURE LIST DERIVATION SECTION (REFERENCE PICTURE LISTGENERATION MEANS)

20 HEADER CODING SECTION

21 PICTURE CODING SECTION

23 REFERENCE PICTURE INFORMATION CODING SECTION (REFERENCE PICTUREINFORMATION CODING MECHANISM)

24 REFERENCE PICTURE SET DECISION SECTION (REFERENCE PICTURE SETDECISION MECHANISM)

25 REFERENCE PICTURE LIST DECISION SECTION

What is claimed is:
 1. An image decoding method comprising: receiving abitstream comprising one or more coding parameters used in decoding atarget picture of a video sequence deriving, based on the bitstream, areference picture set to be applied to the target picture; generating areference picture list based on reference picture list (RPL)modification information decoded from a slice header and the referencepicture set; determining a value of a first flag included in the one ormore coding parameters, the first flag indicating whether informationregarding list sorting is present within the slice header; omittingdecoding of a part of information included in the RPL modificationinformation, wherein the RPL modification information includes at leasta reference picture list sorting presence or absence flag and areference list sorting order, and wherein decoding of the referencepicture list sorting presence or absence flag and the reference listsorting order is omitted based on a number of current picture referablepictures and the value of the first flag; generating a predicted imagebased on a reference picture included in the generated reference picturelist; and generating a decoded image of the target picture based on thepredicted image.
 2. The method of claim 1, wherein the reference picturelist sorting presence or absence flag is decoded from the bitstream upondetermining that the number of current picture referable pictures isgreater than 1, and that the first flag has a non-zero value.
 3. Themethod of claim 1, wherein the one or more coding parameters areincluded in a sequence parameter set (SPS).
 4. The method of claim 3,further comprising decoding the target picture based on the predictedimage.